- Killing is bad
- Killing constitutes revenge
- Killing is unbecoming of society
- Killing is disturbing
Yes, they're from great thinkers, but on their own they don't constitute much of an argument, nor are they particularly elucidating.
The devils advocate might respond:
- pleasant dissuasion is oxymoronic
- what is justice without revenge?
- there's value in symbolism (a hornets nest of an argument, I willingly admit, but one that I think is nonetheless undervalued)
- the disturbing nature of killing has little to do with anything
- we recognize that lethal force is legitimate in self-defense, so clearly some intentional killing is acceptable. This is at odds with the sweeping condemnation of killing in the selected quotes.
- the comparison of capital punishment to murder is fallacious since the former is done with careful attention to impartiality (in principle, anyway)
- the state is founded on the monopoly of violence
I'm as French as you are, cher ami, but there are few things I cherish less about our country than our penchant for empty grandiloquence (exhibit A: Bernard Henri Levi). Appeal to authority does not a strong argument make; just because Victor Hugo said it doesn't make it true. It also pays to remember that many of the individuals you cite are reacting to a very different brand of capital punishment: the kind in which people were tortured in the public square.
To be clear, these intellecutals do have interesting things to say on the subject, but a handful of quotes does little to advance the debate. What we have here are just pretty words, I'm afraid.